CN112585995B

CN112585995B - Method and loudspeaker for displacement measurement in a driver

Info

Publication number: CN112585995B
Application number: CN201880096485.5A
Authority: CN
Inventors: 弗雷德里克·斯科夫高
Original assignee: Goertek Inc
Current assignee: Goertek Inc
Priority date: 2018-09-06
Filing date: 2018-09-06
Publication date: 2023-04-25
Anticipated expiration: 2038-09-06
Also published as: WO2020047791A1; US20210021918A1; CN112585995A

Abstract

The invention discloses a method and a loudspeaker for displacement measurement in a driver. The method comprises the following steps: selecting a fixed position for securing the optical sensor inside or outside the drive; placing the optical sensor by using the fixed position, wherein the optical sensor is located within a line of sight of and facing a moving part of the drive; receiving, by the optical sensor, light reflected or emitted by the moving part; and processing, by a processing device, the signal of the light received from the optical sensor, calculating the displacement of the moving part.

Description

Method and loudspeaker for displacement measurement in a driver

Technical Field

The present invention relates to the technical field of audio technology, and more particularly to a method and a loudspeaker for displacement measurement in a driver.

Background

Displacement measurements may be used to improve drive performance. For example, in a driver of an electronic device such as a speaker, displacement measurements and predictions may be used as inputs to some digital signal processing features. For example, a displacement limiter may be provided and limit the actuator when it is driven to make a loud sound beyond a maximum safe displacement or movement.

Currently, displacement measurement methods are cumbersome and take up a lot of space, which can limit the design and integration of the driver. Furthermore, the performance of the drive may be affected due to the placement of additional components on the moving part.

Disclosure of Invention

It is an object of the present invention to provide a new solution for displacement measurement in a drive.

According to a first aspect of the present invention there is provided a method for displacement measurement in a drive, the method comprising: selecting a fixed position for securing the optical sensor inside or outside the drive; placing an optical sensor by using a fixed position, wherein the optical sensor is in line of sight of and facing a moving part of the drive; receiving, by an optical sensor, light reflected or emitted by the moving part; and processing the signal of the light received from the optical sensor by the processing means to calculate the displacement of the moving part.

According to a second aspect of the present invention, there is provided a speaker comprising: a housing; a speaker unit installed in the housing, the speaker unit including a moving part; and an optical sensor placed by using the selected fixed position of the speaker and facing the moving member within the line of sight of the moving member, wherein the optical sensor receives light reflected or emitted by the moving member and transmits a signal for the light to an internal or external processing device so that the processing device processes the signal of the light received from the optical sensor to calculate the displacement of the moving member.

According to embodiments of the present disclosure, the displacement measurement is non-invasive and thus does not affect the performance of the drive.

Other features of the present invention and its advantages will become apparent from the following detailed description of exemplary embodiments according to the present invention, which refers to the accompanying drawings.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention.

Fig. 1 is an illustrative flow chart of a method for drive displacement measurement according to a first embodiment of the disclosure.

Fig. 2 is a schematic diagram showing an arrangement of a sensor for displacement measurement according to a second embodiment of the present disclosure.

Fig. 3 is a schematic diagram showing an arrangement of a sensor for displacement measurement according to a third embodiment of the present disclosure.

Fig. 4 is a schematic diagram showing an arrangement of a sensor for displacement measurement according to a fourth embodiment of the present disclosure.

Fig. 5 is a schematic diagram showing an arrangement of a sensor for displacement measurement according to a fifth embodiment of the present disclosure.

Fig. 6 is a schematic diagram showing an arrangement of a sensor for displacement measurement according to a sixth embodiment of the present disclosure.

Detailed Description

Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangement of the components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless it is specifically stated otherwise.

The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

Techniques, methods, and apparatus as known to one of ordinary skill in the relevant art may not be discussed in detail, but are intended to be part of the specification where appropriate.

In all examples described and discussed herein, any particular value should be construed as being merely illustrative and not limiting. Thus, other examples of the exemplary embodiments may have different values.

Note that in the following figures, like reference numerals and letters refer to like items, and thus once an item is defined in one figure, it may not be necessary to discuss it further in the following figures.

Fig. 1 is an illustrative flow chart of a method for displacement measurement in a drive according to a first embodiment of the present disclosure.

In step S1100, a fixed position for fastening the optical sensor inside or outside the drive is selected.

In step S1200, the optical sensor is placed by using the fixed position. The optical sensor is within line of sight of and facing the moving part of the drive.

In step S1300, the optical sensor receives light reflected or emitted by the moving member.

In step S1400, the processing means processes the signal for the light received from the optical sensor, thereby calculating the displacement of the moving part.

The optical sensor is non-invasive here and therefore does not affect the performance of the drive. Furthermore, the optical sensor may directly monitor the movement of the moving part of the drive. Thus, the result may directly indicate the movement position of the moving member. As a result, the measurement output can directly and accurately represent the extent to which the driver is approaching its maximum safe displacement. The displacement measurement may indicate the degree of entrainment of the driver and achieve bass enhancement without causing distortion.

Such accurate displacement measurements may enable a designer to set accurate margins for the drive. Otherwise, due to unknown factors such as changes in material properties, changes in system parts (e.g., back volume and driver parts), aging of materials/changes in material parameters over time, changes in room acoustics, designers must add substantial safety margins. Because displacement measurements in an embodiment may not depend on the operation of the drive, these unknowns will have no or little effect on the measurements.

In this embodiment, such direct displacement measurement enables the designer to obtain more performance from an acoustic system with active speakers. Furthermore, such accurate displacement measurements may enable room compensation features, since a designer may utilize the displacement of the drive at different frequencies to evaluate room properties. Here, the driver may be a speaker unit of the speaker.

Based on the embodiment shown in fig. 1, another embodiment of the present disclosure further includes:

in step S1100, selecting a fixed location includes: selecting at least one of the following positions as a fixed position: a position at the pole shoe of the magnet system of the drive, a position at the basin stand of the drive, and a position outside the drive.

For example, selecting the fixed location further includes: the fastening portion of the basin stand of the driver is selected as the fixing position, which fastening portion is used for fastening the driver to the housing. Selecting the fastening portion of the basin stand of the driver as the fixed position may further include: the upper surface or the lower surface of the part where the bolt hole of the basin stand is positioned is selected as the fastening part of the basin stand.

The fastening part of the frame of the driver for fastening the driver to the housing is usually the most robust part of the loudspeaker. When it is fastened to the housing, the component does not move and can provide a stable base for the optical sensor. Furthermore, the mounting of the optical sensor may take the same way as the mounting of the driver into the housing, for example a bolt-and-nut mounting. In this way, the process of installing the optical sensor can be simplified.

In another example, selecting the fixed location may further include: the position on the outer housing of the drive is selected as the fixed position. This gives the designer more freedom to choose where to place the optical sensor than a solution to choose the position in the drive.

In step S1200, placing the optical sensor may further include: forming a support element; and one end of the supporting element is attached at a fixed position and the other end of the supporting element is connected with the optical sensor. For example, forming the support element may include: a support element is formed having at least two branches which are not parallel and which are radial from the optical sensor. This provides a relatively stable support for the optical sensor. Here, forming the support member may further include: at least two branches of the support element are arranged in a plane having a projection plane parallel to the vibration direction of the moving part.

Since displacement in the vibration direction is of primary concern in the present invention, this structure will provide a firm support in that direction so that the sensing of the optical sensor can output relatively accurate results.

In one example, placing the optical sensor may further include: the optical sensor is placed in an oblique direction so as to face the moving member. The tilt direction is a direction inclined with respect to the main axis of the drive or an end face of the drive perpendicular to the main axis. In this way, the designer will have more freedom to place the optical sensor.

In another example, placing the optical sensor may further include: the optical sensor is placed in a cavity of the driver distal to a terminal of the driver. In this way, the optical sensor does not conflict with the arrangement of the terminals and/or the interference between them (electromagnetically or in the design room) is reduced.

In yet another example, the location at the pole piece is a location at an inner surface of a hollow structure inside the pole piece and a location at a lower end of the pole piece near a diaphragm of the driver, and the moving component is an inner surface of a voice coil former of the driver. Thus, placing the optical sensor in a fixed position may further comprise: the optical sensor is placed inside the hollow structure of the pole piece by a support element and is arranged facing the inner surface of the voice coil former. On the one hand, in general, no additional elements are placed inside the pole shoe. Thus, this arrangement will take advantage of spare space in the drive and no additional space is required. Furthermore, the moving member moves with respect to the pole piece and placing the optical sensor on the pole piece provides accurate and direct displacement results. Thus, the measurement may be more accurate.

For example, placing the optical sensor at a fixed location may further include: the optical sensor is arranged such that a portion of the optical sensor is pressed against the lower end of the pole piece (see example in fig. 2). This will increase the robustness of the optical sensor support.

In one example, the moving part is a voice coil former, a voice coil, or a diaphragm of a speaker unit. The optical sensor is in direct line of sight of the voice coil former, voice coil or diaphragm and tracks their movement. Preferably, the optical sensor is facing the voice coil former. The voice coil former and voice coil are directly coupled to the diaphragm, and their movements may directly reflect the movements of the diaphragm.

In this regard, the method may further comprise: selecting a moving part as a voice coil of the driver; and/or selecting the moving part as an inner surface of a voice coil former of the driver; and/or selecting the moving part as an outer surface of the voice coil former of the driver, the outer surface being at a lower portion of the voice coil former, and the lower portion being adjacent to the diaphragm of the driver; and/or selecting the moving part as a front surface of the diaphragm of the actuator or as an inner surface of the diaphragm of the actuator. Thus, step S1300 may include: light reflected or emitted by the predetermined area of the voice coil, the predetermined area of the voice coil former, and/or the predetermined area of the diaphragm is received by the optical sensor. The preset area is an area that enables the optical sensor to scan light from the moving part. Also in this solution, displacement prediction can be achieved by monitoring the driver's own moving parts, so that no further moving parts need to be added to the speaker unit.

The optical sensor may be placed anywhere within the line of sight of the moving part of the drive. This eliminates the need to add components to the moving part to sense its movement.

The processing means may be separate from the optical sensor or integrated with the optical sensor. Those skilled in the art will recognize that the processing means may be implemented in various ways. It may be implemented by discrete devices, ASICs, programmable devices (e.g., PLD, DSP, FPGA). Alternatively, it may be implemented in a combination of a processing unit such as a CPU or MPU with a memory, wherein instructions are stored in the memory and used to control the processing unit to perform the corresponding operations. The present disclosure is not limited in their implementation in this regard. Those skilled in the art can, with consideration of cost, market conditions, and the like, select an embodiment under the teachings of the present disclosure.

The optical sensor may perform any suitable type of optical sensing. Some optical sensors do not require a specific light source for sensing.

In an example, the optical sensor is a doppler-based optical sensor. It senses the doppler effect of the received light. The processing means calculates the displacement based on the doppler effect of the received light.

In another example, a tracking pattern may be provided on the surface of the moving part. The tracking pattern may be any pattern that is capable of indicating movement of the moving part. For example, it may be a series of lines arranged along the moving direction of the moving member, the thickness of which indicates the moving position of the moving member.

The processing means may take pictures of the tracking pattern at short intervals based on the received light and calculate the displacement by correlating the pictures with each other.

In yet another example, a fade map may be provided on the surface of the moving part. The processing means may calculate the displacement by measuring the received light reflected by the gradient map.

Other optical sensors may use their own light sources for sensing.

For example, in the method of this embodiment, the light emitters may be placed in additional fixed positions within the line of sight of the moving parts of the driver. The light emitter emits light to be reflected or emitted by the moving part. The light emitters may be placed on the same side of the moving part or on the opposite side of the optical sensor with respect to the moving part. Thus, the optical sensor may receive light reflected or emitted by the moving part. In the latter case, the moving part is transparent to the light to be sensed by the optical sensor.

In one example, the fixed location and the additional fixed location are the same location, and the light emitter and the optical sensor are integrated and placed at the same location. For example, the optical sensor and the light emitter are those of an optical encoder.

In another example, the processing device calculates the displacement based on the intensity of the received light.

Those skilled in the art will recognize that a light source (light emitter) may also be provided for the optical sensor illustrated in the example, which does not require a specific light source for sensing.

The fixed location may be on a fixed support member of the drive. Similarly, the fixed location may also be on a fixed support member inside the drive. Alternatively, it may be on a fixed structure external to the driver, for example on a fixed structure on the housing of the loudspeaker. Here, the optical sensor can be removable and/or replaceable. As a result, failure of the displacement measurement may not affect the performance of the drive.

The light emitted by the light emitter and/or received by the optical sensor may be in the invisible spectrum. In this respect, the operation of the displacement measurement does not disturb the user.

Fig. 2-6 schematically illustrate an arrangement of sensors for displacement measurement according to embodiments of the present disclosure. In fig. 2-6, a speaker to which the above-described embodiments are applied is provided. The description of the embodiments repeated with the first embodiment will be omitted.

The speaker may include: a housing 300; a speaker unit 100 mounted in the housing 300; and an

optical sensor

201, 211, 221, 231, or 241. The speaker unit 100 includes a moving part. The housing 300 is shown in fig. 6 and omitted in fig. 2-5.

The

optical sensor

201, 211, 221, 231 or 241 is placed by using the fixed

position

202, 212, 222, 232 or 242 of the selected speaker and is within the line of sight of and facing the moving part. The

optical sensor

201, 211, 221, 231, or 241 receives light reflected or emitted by the moving part. The speaker may also include an internal or external processing device 400. The

optical sensor

201, 211, 221, 231 or 241 transmits a signal for light to an internal or external processing device so that the processing device processes the signal of light received from the

optical sensor

201, 211, 221, 231 or 241 to calculate the displacement of the moving part. The speaker unit 100 is a driver as described above. The processing means 400 is shown in fig. 2 and omitted in fig. 3-6.

The

optical sensor

201, 211, 221, 231 or 241 may be placed in a

fixed position

202, 212, 222, 232 or 242 by a

support element

2011, 2111, 2211, 2311 or 2411. For example, the support element has at least two branches which are not parallel and which are radial from the optical sensor. Alternatively, at least two branches of the support element are arranged in a plane having a projection plane parallel to the vibration direction of the moving part.

As shown in fig. 2 to 6, the speaker unit 100 includes a magnet system 101, terminals 102, a damper 103, a bobbin 104, a folder 105, a diaphragm 106, a voice coil bobbin 107, and a voice coil 108. Here, the moving member may be a voice coil bobbin 107, a voice coil 108, or a diaphragm 106.

For example, the fixed position is a position 202 at the pole piece 1011 of the magnet system 101 of the speaker unit, a

position

212, 222 or 232 at the basin stand 212 of the speaker unit or a position 242 outside the speaker unit 100. Fig. 2-6 show several examples of different arrangements.

As shown in fig. 2, the fixed position is a position 202 at pole piece (or T-iron) 1011. The location 202 at the pole piece 1011 is a location 202 at the inner surface of the hollow structure inside the pole piece. The hollow structure may be a through hole as shown in fig. 2 or a recess at the lower end of the pole piece 1011 towards the diaphragm 106. The location 202 may be at the lower end of the pole piece near the diaphragm 106 of the speaker unit 100. Here, the lower end means that it can provide support through the lower end of the pole piece. The moving part is an inner surface of the voice coil bobbin 107 of the speaker unit 100. The optical sensor 201 is placed inside the hollow structure by the support member 2011 and is arranged to face the inner surface of the voice coil bobbin 107. The support element 2011 may be a metal frame or a plastic frame. One end of the support member 2011 is placed on the fixed support member 202, and the optical sensor 201 is supported on the other end of the support member 2011. Because the voice coil former 107 moves relative to the magnet system 101 to drive the diaphragm 106, the result of placing the optical sensor 201 on the pole piece 1011 of the magnet system 101 will directly reflect the displacement relative to the magnet system 101 and eliminate the effect of the smaller displacement of the magnet system 101.

In one example, the optical sensor 201 is placed such that a portion of the optical sensor is pressed against the lower end of the pole piece 1011. The support element 2011 and the pole piece 1011 provide a stable support for the optical sensor 201. Errors caused by movement of the optical sensor 201 during sensing may be reduced or eliminated in this manner.

Furthermore, the support element 2011 may have at least two branches, for example three branches, which are not parallel and are radial from the optical sensor 201. This arrangement may increase the stability of the support.

The optical sensor 201 scans an area 203 on the voice coil former 107, which is the inner surface of the voice coil former 107. Typically, the components of the microphone unit are arranged outside the voice coil former and do not use the inner space thereof. In this embodiment, the optical sensor 201 is arranged inside the voice coil former and utilizes unused space. Thus, this design does not increase the overall volume of the speaker unit. Furthermore, the voice coil former 107 is a rigid member, and thus its measurement may be constant. The measurement results may be advantageous for the processing means to determine the state of the diaphragm based on a constant criterion.

In this example, region 203 is the inner surface at the lower portion of voice coil former 107, which is proximate to diaphragm 106. The lower portion of the voice coil former will be connected to and drive the diaphragm 106 in vibration. This arrangement provides more accurate results in cases involving displacement of the diaphragm.

Fig. 3-5 show the fixation position at the basin stand 104 of the speaker unit 100. The fixing position at the tub 104 is at a fastening portion of the tub 104 of the speaker unit 100 for fastening the speaker unit 100 to the case 300. The fastening portion of the tub is an upper surface or a lower surface of the

portion

212, 222 or 232 where the bolt hole of the tub 104 is located.

As shown in fig. 3, the fixed position is the upper surface of the part 212 of the basin stand 104. The optical sensor 211 is fastened to the upper surface of the part 212 of the basin stand 104. The part 212 of the tub 104 is a fastening portion for fastening the speaker unit 100 to the case 300. For example, the tub 104 is fastened to the case 300 by bolts. The fixing member may be a portion 212 where the bolt hole is located. The fastening portion is typically a relatively stable component of the speaker unit and this arrangement will provide a stable support for the optical sensor 211, which may make the sensing result more accurate.

The optical sensor 211 is placed on the part 212 of the basin stand 104 by means of a support element 2111 similar to the support element 2011. The support element 2111 may have at least two branches. In general, the vibration direction of the voice coil bobbin 107 is an up-down direction, which is a direction related to sensing. In this regard, at least two branches of the support element 2111 may be arranged in a plane having a projection plane parallel to the vibration direction. In this way, the support element 2011 may provide a firm support with respect to the sensing plane.

In this example, optical sensor 211 scans region 213 on voice coil former 107. This region 213 is the outer surface of the voice coil former 107. As described above, region 213 may be located at a lower portion of voice coil former 107, which is proximate diaphragm 106.

As shown in fig. 4, the fixed position is the lower surface of the part 222 of the basin stand 104. The optical sensor 221 is fastened to the lower surface of the part 222 of the basin stand 104. In this example, similar to the embodiment of fig. 3, the part 222 of the basin stand 104 is also a fastening portion of the speaker unit 100. The optical sensor 221 is fastened to the fastening portion by a support member 2211. One end of the support member 2211 is placed on the lower surface of the fastening portion, and the optical sensor 221 is placed on the other end of the support member 2211.

The optical sensor 221 is disposed in front of the diaphragm 106 and scans a front surface area 223 of the diaphragm 106. In this case, the optical sensor is mounted outside the drive.

As shown in fig. 5, the fixed position is the upper surface of the part 232 of the basin stand 104. The optical sensor 231 is fastened to the upper surface of the part 212 of the basin stand 104. In this example, similar to the embodiment of fig. 3, the fixed support member 232 is also a fastening portion of the speaker unit 100. The optical sensor 231 is fastened to the fastening portion by a support member 2311. One end of the supporting member 2311 is placed on the upper surface of the fastening portion, and the optical sensor 231 is placed on the other end of the supporting member 2311.

The optical sensor 231 is arranged in an oblique direction such that it is placed towards the inner surface of the diaphragm and scans the inner surface area 203 on the diaphragm 106. The optical sensor 231 is placed inside the speaker unit 100 and is not occupied with a space outside the speaker unit. Here, the optical sensor 231 may not have a light source (light emitter), and may receive light emitted through the diaphragm 106.

In fig. 4 and 5, the

optical sensor

221 or 231 is arranged in an oblique direction so that it faces the moving member 106.

As shown in fig. 6, the fixed position is a position 242 outside the speaker unit 100. The optical sensor 241 is fastened by a support element 2411 at a position 242 on the housing 300. The fixed support part 242 is outside the speaker unit 100. Optical sensor 241 scans region 243 on voice coil former 107. The region 243 may be an outer surface of the voice coil former 107 at a lower portion thereof that is adjacent to the diaphragm 106.

As shown in fig. 3-6, the optical sensor is arranged in a cavity of the speaker unit remote from the terminal 102 so that it does not interfere with the arrangement of the terminal 102 and its associated circuitry.

The voice coil 108 is wound around the voice coil bobbin 107. Thus, in the above-described embodiments, the optical sensor may also be arranged to scan an area on the voice coil 108, similar to the scanning of the voice coil former 107.

As described above, the

optical sensor

201, 211, 221, 231 or 24 may be a doppler-based optical sensor, and the processing means may calculate the displacement based on the doppler effect of the received light.

For example, a tracking pattern is provided on the surface of a moving member such as the voice coil bobbin 107, the voice coil 108, or the diaphragm 106. The processing means takes pictures of the tracking pattern at short intervals based on the received light and correlates the pictures to calculate the displacement.

For example, a gradation map is provided on the surface of a moving part such as the voice coil bobbin 107, the voice coil 108, or the diaphragm 106. The processing means calculate the displacement by measuring the received light reflected by the gradient map.

For example, the speaker may further include: a light emitter (not shown) placed in an additional fixed position of the speaker and within the line of sight of the moving parts of the driver. The light emitter emits light to be reflected or emitted by the moving part.

For example, the fixed location and the additional fixed location are the same location, and the light emitter and the optical sensor are integrated and placed at the same location. In this regard, the optical sensor and the light emitter may be those of an optical encoder.

For example, the processing means calculates the displacement based on the intensity of the received light.

For example, the light sensed or received by the optical sensor may be in the invisible spectrum.

Although specific embodiments of the invention have been described in detail by way of example, it will be appreciated by those skilled in the art that the above-described embodiments are for illustration only and are not intended to limit the scope of the invention.

Claims

1. A method for displacement measurement in a drive, comprising:

selecting a fixed position for fastening the optical sensor outside the driver, wherein the fixed position is a position that is located outside in a circumferential direction of a moving part of the driver and on an outer housing of the driver;

placing the optical sensor by using the fixed position, wherein the optical sensor is located within the line of sight of and facing a moving part of the driver, wherein the moving part is selected as an outer surface of a voice coil former of the driver, the outer surface is located at a lower portion of the voice coil former and provided with a tracking pattern thereon capable of indicating movement of the moving part, and the lower portion is close to a diaphragm of the driver;

receiving, by the optical sensor, light reflected or emitted by the moving part; and

pictures of the tracking pattern are taken at intervals based on the received light by a processing device and correlated to calculate a displacement of the moving part.

2. The method of claim 1, wherein placing the optical sensor further comprises:

forming a support element; and

one end of the supporting element is attached to the fixed position, and the other end of the supporting element is connected with the optical sensor.

3. The method of claim 2, wherein forming the support element comprises:

the support element is formed with at least two branches which are not parallel and which start radially from the optical sensor.

4. The method of claim 3, wherein forming the support member further comprises:

at least two branches of the support element are arranged in a plane having a projection plane parallel to the vibration direction of the moving part.

5. A speaker, comprising:

a housing;

a speaker unit mounted in the housing, the speaker unit including a moving member, wherein the moving member is selected as an outer surface of a voice coil former of the speaker unit, the outer surface is located at a lower portion of the voice coil former and provided with a tracking pattern capable of indicating movement of the moving member, and the lower portion is close to a diaphragm of the speaker unit; and

an optical sensor placed by using a fixed position of the speaker selected, wherein the fixed position is a position that is located outside in a circumferential direction of the moving member and on the housing, and the optical sensor is within a line of sight of the moving member and faces the moving member, wherein the optical sensor receives light reflected or emitted by the moving member and sends a signal for the light to an internal or external processing device so that the processing device takes pictures of the tracking pattern at intervals based on the received light, and correlates the pictures to calculate a displacement of the moving member.

6. The loudspeaker of claim 5, wherein the optical sensor is placed in the fixed position by a support member,

the support element having at least two branches which are not parallel and which are radial from the optical sensor,

wherein at least two branches of the support element are arranged in a plane having a projection plane parallel to the vibration direction of the moving part.